Though slavery was officially ended after the Civil War, injustices against black people continued. This poem centers on one of the most graphic and terrible racial injustices of the post-Civil War era—lynching. "Song for a Dark Girl" is abundantly clear about one thing: in the world of this poem, black people suffer, and a white Jesus doesn't seem to care.
This poem comments on racism subtly, through language and irony. But Hughes won't hit you over the head with it, because he knows it's more effective to be subtle.
This poem doesn't focus on race as much as people think. It's really about personal grief.